Honeywell smart transmitter design makes communication card swap easy

It was bound to happen sooner or later.

I took a call from a customer who needed to replace a garden variety differential pressure transmitter… with one exception: He needed Honeywell’s DE digital protocol for communicating to his DCS. The DE protocol is still great, but since so many installations today use HART or Foundation Fieldbus, all of our in-stock pressure transmitters had a HART communication card – a critical mismatch to what the customer needed.

A year ago, we would have been stuck rush-ordering a unit from the factory, with all the attendant delays and expediting charges, because you couldn’t swap out a comms card without making the transmitter’s hazardous approval invalid.

What could we do?

With the modular design of the latest Honeywell SmartLine ST700 and ST800 transmitters, it’s easy. I took a stock transmitter off the Lesman shelf, and our shop technician swapped the existing HART communication card with a DE card. And the transmitter was ready for will-call pickup in minutes!

As you can see in the diagram, you access the communications card through a crew cover, remove two retaining screws, and take off the display module. The key to being able to swap out the cards is that with the new series, the hazardous area approval is provided for the comms card itself, and NOT for the card pre-assembled into a transmitter, as it was for older ST3000 series. New Honeywell SmartLine DE, HART, and Foundation Fieldbus communication cards have the necessary approvals for installation into any ST700 and ST800 transmitter.

This quick-swap modularity could be of value if you get your equipment on skids. We’ve heard that sometimes the plant’s communication protocol spec doesn’t get passed to the procurement chain, and the equipment shows up talking the wrong protocol. That can be fixed quickly by swapping out the comms cards. No need to return the transmitters.

The best part? I asked the shop tech how long it took to swap out the cards.

“It’d take longer to pack the transmitter in a shipping carton and box it up than it takes to unscrew the transmitter screw cover, remove one card, and put the other back in.”